Weapon design - how much can you lighten an artillery barrel?

[BraselC5048]

Going about designing weapons for my TL 8+^ campaign, I'm trying to figure out how much I can lighten the 105mm recoilless rifle, which is pretty similar to the M40 from High Tech. It's a limited production weapon; the Navy only needs to put a compliment of 2-8 weapons shipboard (4-ish on maybe 80 cruisers, a larger number on 80 battleships, smaller number on destroyers and frigates), and enough to equip two marine divisions, which rarely see combat, mostly sitting in garrison scattered between different planets, even during wartime. Even at most 100 weapons a year during wartime is all that would be needed, and if limited stocks are built up during peacetime, it may go in and out of production as the need arrises.

Lightening the tripod is easy - just make it out of the same high strength titanium alloy the navy builds their ships out of, they could likely simply machine it out of scraps from the dockyards, a single cruiser has at least 20,000 tons of the stuff.

My question is how much would using special high strength, but expensive, alloys for the barrel allow you make it lighter? I would assume it's possible, but not actually done today due to cost for a massive number of weapons. The Navy in my campaign enjoys the luxury of having a very small weapon loss rate coupled with a non-expanding number required, so they can afford to spend more per weapon.

So how much, if any weapon experts would like to weigh in. 25%? 50%? I don't really have a number to go on.

[doulos05]

Originally Posted by BraselC5048

Going about designing weapons for my TL 8+^ campaign, I'm trying to figure out how much I can lighten the 105mm recoilless rifle, which is pretty similar to the M40 from High Tech. It's a limited production weapon; the Navy only needs to put a compliment of 2-8 weapons shipboard (4-ish on maybe 80 cruisers, a larger number on 80 battleships, smaller number on destroyers and frigates), and enough to equip two marine divisions, which rarely see combat, mostly sitting in garrison scattered between different planets, even during wartime. Even at most 100 weapons a year during wartime is all that would be needed, and if limited stocks are built up during peacetime, it may go in and out of production as the need arrises.

80 cruisers x 4
80 battleships x 8
160 destroyers x 2
160 frigates x 2
That's 1600 on just the ships. You're moving out of the realm of "limited production" for a shipboard weapon with those numbers. For reference, the 5"/38 dual purpose gun produced for World War 2 had, at the end of the war, a total of ~3,600 installations (I'm counting the dual mounts as double since what we care about is engineering the barrels). Given that the majority are distributed on destroyers in that count and given that those ships suffered higher losses and I'm not sure if he's accounting for sunk ships in his installation count, double it. We're still within an order of magnitude. (Source) and that's when we were on a crazy-high wartime footing. That said, given TL8^ manufacturing techniques, there's no real reason why "mass production" has to mean "lower quality, so we built it heavier".

[Nereidalbel]

Given the "+" and "^" in your tech, I don't see why you couldn't have barrels made of basic frames wrapped in graphene. The stuff is ultra light and ridiculously strong.

[doulos05]

Originally Posted by Nereidalbel

Given the "+" and "^" in your tech, I don't see why you couldn't have barrels made of basic frames wrapped in graphene. The stuff is ultra light and ridiculously strong.

But is it conceivable that it's cheap?

[Anthony]

Originally Posted by BraselC5048

My question is how much would using special high strength, but expensive, alloys for the barrel allow you make it lighter? I would assume it's possible, but not actually done today due to cost for a massive number of weapons.

The big problem is that there isn't much you can do to make the ammunition lighter (and if you only want a small ammunition capacity, just use a missile launcher).

[Nereidalbel]

Originally Posted by doulos05

But is it conceivable that it's cheap?

Graphene is made from graphite, which is cheap enough at TL8. Given that you have the plus, yes, it can be mass-produced for relatively low cost. If you get the barrels pre-fabricated with the stuff, costs can be lowered even more.

The real question would be "why are your people not using this for body armor?!?"

[BraselC5048]

Originally Posted by doulos05

80 cruisers x 4
80 battleships x 8
160 destroyers x 2
160 frigates x 2
That's 1600 on just the ships. You're moving out of the realm of "limited production" for a shipboard weapon with those numbers. For reference, the 5"/38 dual purpose gun produced for World War 2 had, at the end of the war, a total of ~3,600 installations (I'm counting the dual mounts as double since what we care about is engineering the barrels). Given that the majority are distributed on destroyers in that count and given that those ships suffered higher losses and I'm not sure if he's accounting for sunk ships in his installation count, double it. We're still within an order of magnitude. (Source) and that's when we were on a crazy-high wartime footing. That said, given TL8^ manufacturing techniques, there's no real reason why "mass production" has to mean "lower quality, so we built it heavier".

I never established firm numbers, but you could likely cut the number of destroyers and frigates in half (perhaps 40? frigates?). It's not a starship weapon - it's an infantry support weapon for the storerooms. The barrel only weighs 220-240 pounds, and the tripod on the real weapon it's based on 200 lbs. It's nowhere near as big and heavy as a US 5"/38 DP. Starships stay in service until lost for some reason or another, or (very rarely) old age. The oldest 4 ships in the Navy are nearing a full century of service, and 30-40 years old for a starship is considered "late middle aged." I figure no more than 2500 weapons in existence, and it's perfectly likely a fair chunk of them date from the first batch produced, easily a decade ago. It likely took the Imperial Naval Arsenal a few years to turn out enough to equip the fleet. It's likely there's only one set of tooling, and it's impossible to make more than one barrel at once. And even then it's likely idle much of the time even during a war, simply because there's no new demand. The Marine's aren't expanding, there have been only 6 divisions for maybe a century (2 shipboard, 2 guarding installations, 2 sitting in garrisons ready to be used), and there have only been a most a handful of occasions where a Maine division actually was on the same planet at the same time. There's simply no reason to have more, they're not regular frontline troops, they're the Navy's ground troops, which means an Admiral can dispose of a battalion without having to get the Army to go along. If they're on a planet likely to be attacked, the Navy most likely would evacuate them and let the Army do the job. Even then, it's rare for a Marine division, or portions of it, to see any fighting where it's not a quick, short and sharp battle. The only reason to make more is to replace the ones on a ship that's lost or in the event that the Navy builds a new ship, but the Navy isn't really expanding much.

(Inter-service relationships border on the "dysfunctional, each do their own thing unless the Army needs transport, and when running in supplies." There are some extremely advanced and highly classified explosive production techniques the Navy has no intention of ever sharing with anybody in the Army, and it's been 15 years now.)

[The_Ryujin]

You could just say that they're made from TL9 advanced metallic laminate which would let you effectively make the barrels 50% stronger for the same weight or you can divide it's weight by 1.5 for the same level of strength.

[doulos05]

Originally Posted by BraselC5048

I never established firm numbers, but you could likely cut the number of destroyers and frigates in half (perhaps 40? frigates?).

Assuming a wet-water navy model, it would be very odd to have fewer escorts than you have capital ships. That's for 2 reasons. 1) Escorts are meant to maintain separation between the capital ships and the enemy. In order to do that, you have to spread a web of escorts out in all directions from the capital ships. 2) You use escorts of missions smaller than capital ship missions. You don't need to send a battleship to escort a merchant convey to protect it against pirates. You probably don't need to send a battleship to "show the flag" at a planet that's threatening to rebel. You use destroyers and frigates (maybe cruisers) for that.

It's not a starship weapon - it's an infantry support weapon for the storerooms. The barrel only weighs 220-240 pounds, and the tripod on the real weapon it's based on 200 lbs. It's nowhere near as big and heavy as a US 5"/38 DP.

Wait, so are these mounted on the ships or held in the armory to loan out to marine detachments requiring additional firepower?

Starships stay in service until lost for some reason or another, or (very rarely) old age. The oldest 4 ships in the Navy are nearing a full century of service, and 30-40 years old for a starship is considered "late middle aged." I figure no more than 2500 weapons in existence, and it's perfectly likely a fair chunk of them date from the first batch produced, easily a decade ago. It likely took the Imperial Naval Arsenal a few years to turn out enough to equip the fleet. It's likely there's only one set of tooling, and it's impossible to make more than one barrel at once. And even then it's likely idle much of the time even during a war, simply because there's no new demand. The Marine's aren't expanding, there have been only 6 divisions for maybe a century (2 shipboard, 2 guarding installations, 2 sitting in garrisons ready to be used), and there have only been a most a handful of occasions where a Maine division actually was on the same planet at the same time. There's simply no reason to have more, they're not regular frontline troops, they're the Navy's ground troops, which means an Admiral can dispose of a battalion without having to get the Army to go along. If they're on a planet likely to be attacked, the Navy most likely would evacuate them and let the Army do the job. Even then, it's rare for a Marine division, or portions of it, to see any fighting where it's not a quick, short and sharp battle. The only reason to make more is to replace the ones on a ship that's lost or in the event that the Navy builds a new ship, but the Navy isn't really expanding much.

(Inter-service relationships border on the "dysfunctional, each do their own thing unless the Army needs transport, and when running in supplies." There are some extremely advanced and highly classified explosive production techniques the Navy has no intention of ever sharing with anybody in the Army, and it's been 15 years now.)

But if they're deployed from the ship armory, you might have a higher loss rate because you could lose one dirtside. Though I'll grant you that it wouldn't be much more.

[malloyd]

Originally Posted by BraselC5048

So how much, if any weapon experts would like to weigh in. 25%? 50%? I don't really have a number to go on.

Presumably by the ratio of the tensile strengths per unit weight. Steel alloys are actually pretty good at that, which is after all why we use them. Some expensive steel alloys and treatment processes will get you a factor of 1.5 over more typical alloys ones, but that's probably about all you can hope for, especially under the rather harsh conditions of the interior of a gun barrel. There are alloys that *claim* to outperform the best high nickel steels but numbers are usually not forthcoming to back those claims up. Though I suppose when you have more nickel than iron, and some of them do, it's not technically steel anymore.

On a more theoretical level, for actual materials you can obtain in multi-gram quantities, you can beat steel strength to weight by a factor of 8 or 10, though the best values are for fibers, which probably mean you need to embed them in something to make them into a gun barrel. The best theoretical materials, like those carbon nanotubes or graphine sheets will claim factors of up to about 200, but I strongly doubt if anybody ever manufactures bulk samples they will be anywhere near that good. It's actually a general characteristic of materials that tiny whiskers are an order of magnitude stronger than anything you can get in bulk, simply because they are too small to have scratches or other flaws.